The deaths of seven young people in Scotland are believed to be linked to a batch of fake ecstasy tablets thought to contain toxic chemicals, according to police.

An 18-year-old woman in Alexandria, West Dunbartonshire, died on Tuesday morning and three male friends, aged 18, 21 and 25, were admitted to hospital after taking pills they believed to be ecstasy. The 25-year-old is still receiving treatment.

Police have warned that the suspect pills are green in colour and stamped with a Rolex crown logo, and that some have been found to contain the dangerous stimulant paramethoxyamphetamine, known as PMA. PMA is known to cause extremely high body temperatures, hallucinations and convulsions.

Six other deaths in Glasgow, Lanarkshire and Ayrshire during the past two months have been linked to the pills.

Police are also warning of a white pill with the Mitsubishi logo imprinted on it, found to contain the chemicals 5IT or AMT, and a yellow tablet with a star logo.

Officers in the north of Scotland recovered a large quantity of fake ecstasy tablets at a house in Aberdeen on Wednesday. These tablets are also green but with a Heineken logo.

Police are keen to make the warning public before this weekend's T in the Park music festival at Balado in Perth and Kinross.

Some of the other fake tablets are white or yellow with a Mitsubishi or star logo. Photograph: Police Scotland/PA

Superintendent Grahame Clarke from Police Scotland's western division said: "An investigation is under way and our inquiries have so far revealed that the woman, along with three friends, had taken what they thought were ecstasy tablets. The tablets were described as green with a Rolex crown logo stamped on them.

"Public warnings have been issued recently in relation to the dangers of taking ecstasy, or indeed tablets being passed off as ecstasy. They are illegal and could contain a cocktail of toxic ingredients.

"We have yet to establish if this particular pill is to blame for the death of this young woman, but the fact that she and her friends took pills described as green and with a Rolex stamp on it causes us real concern.

"The exact contents of the pills are unknown but they could contain dangerous chemicals and users need to be aware of the dangers and understand the devastating effect they can have."

Chief Inspector George MacDonald, based in Aberdeen, said following Wednesday's seizure: "The exact contents of these particular pills are unknown at this time. What we have found is that they contain more than one class C drug as well as another dangerous substance, PMA.

"While these tablets do not feature the distinctive Rolex logo found on those in the Glasgow area, they do contain the same toxic substance. The impact of taking a drug you do not know the exact content of can be extremely dangerous and fatal in some cases.

"Taking it just once can be one time too many and I would urge people to avoid any such pills or drugs and report any information to the police."

People taking the fake pills can experience symptoms including high temperature, aggression and muscle pains as well as hallucinations and excitability, according to doctors.

Richard Stevenson, a doctor in emergency medicine at Glasgow Royal Infirmary, said: "These symptoms are treatable if help is sought early. I would urge anyone who begins to feel unwell, or feels a more intense high than usual after taking any drug which they think is ecstasy or not, to seek immediate medical help."